The most commonly used planing hulls for marine purposes have substantially constant dead rises aft of about station 4 or 5, in order to reduce the suction load which can occur with a "hooked" style of hull bottom. With a constant dead rise however the loading between the surface of the hull bottom and the water is usually positive for most of the length of the hull (that is, there is a kinetic energy imparted to the water due to deflection of the particles of water encountered by the hull bottom surface, having a downward component of movement). The trim angle is therefore critical. The pressure pattern however is much higher towards the forebody end of the hull than it is towards the aft end, and consequently most of the dynamic forces which are of use to the hull in ocean-going conditions occur over a relatively short length of the hull, probably not more than 15%. When the dynamic forces are relied upon (as in the usual case), the loading on the "low" side of the hull when deflected by a wave extends over a wider area and the loading on the " high" side extends over a lesser area, thereby establishing a righting force, but over a short length of hull only. It is believed this is one of the limiting features of the standard constant dead rise type of planing hull. If however the loading is more evenly spread over the whole area of the hull, the difference is very much greater and there is a superior righting force.
In my U.S. Pat. No. 4,708,085 entitled "Marine Hull" there is described and claimed a marine hull wherein the shape of the bottom included channels which diverge in a rearward direction, each channel having a surface of such shape that it intercepts and deflects water when the hull is mobile, causing the water so intercepted and deflected to move upwardly and rearwardly with respect to the hull, and then be deflected downwardly by the concave surfaces of the channels and thereby imparting a vertical component of lift well aft of the normal maximum loading area. The rearmost pair of channels defined a "V" shape in plan. Experiments with seagoing craft have proved that the theories appear to be correct, and that a hull with such channels is much more stable and soft riding under rough conditions than a conventional constant dead rise mono-hull type of craft.
With most hulls known to the applicant, there is a serious tendency to pound (hydraulically bottom) as the hull leaves one wave and impacts against the next. Although this pounding effect is worst with hulls having laterally diverging bottom surfaces which are concave, it is nevertheless a serious disability with hulls having straight deadline shapes (in section) and even with those having convex deadline shapes. Even if the forebody is provided with a large dead rise angle, the pounding can still occur rearwardly of the normal area of maximum loading.
Craft made in accordance with the said Patent Application have proved that pounding is largely reduced but nevertheless there still remains a generally unresolved problem with planing hulls, and it is an object of this invention to provide further improvements whereby the tendency to pound can be substantially reduced, even further than with the hull design identified in the specification of said U.S. Pat. No. 4,708,085.